The nominations also set the stage for confirmation fights driven not only by criticism of Hagel and Brennan but by the foreign policy approach they represent.
Hagel, a decorated Vietnam War veteran, shares Obama's aversion to military intervention. White House officials described him as ideally suited to managing the drawdown of U.S. forces in Afghanistan and the shrinking Pentagon budget. But he has attracted fierce criticism from groups that question his support for Israel.
Brennan is a 25-year CIA veteran who has voiced concern over the agency's paramilitary mission and has imposed tighter controls on targeted killing, even while his White House tenure has been marked by a massive increase in the agency's drone campaign.
Four years ago, Brennan withdrew from consideration to be CIA director amid questions about his role as a high-ranking CIA official at a time when the agency employed brutal interrogation techniques - a link certain to resurface when he faces a Senate vote.
Both men are known for their strong personalities and strongly held views. Still, associates described them as comfortable fits for an administration that favors covert action - including Predator drone strikes on al-Qaeda targets and cyber-sabotage of Iran's nuclear plants - over conventional force.
In announcing the nominees, Obama said that their agenda would include "ending the war in Afghanistan and caring for those who have borne the battle, [and] preparing for the full range of threats." He also emphasized their experiences in the lower ranks of the institutions they would run, saying both served overseas and understand firsthand "the consequences of decisions that we make in this town."
Obama avoided one confirmation fight when U.N. Ambassador Susan Rice withdrew from consideration to be secretary of state amid criticism of her role in the aftermath of the attack on the U.S. diplomatic post in Benghazi, Libya. Instead, Obama turned to a compromise pick, Sen. John Kerry (D., Mass.). The former presidential candidate has established relationships with foreign leaders that could help the administration push for tougher sanctions on Iran, expand its pursuit of al-Qaeda beyond Yemen and Pakistan, and deal with the Syrian civil war.
Ben Rhodes, deputy national security adviser for strategic communications, said Obama's selection of Kerry, Hagel, and Brennan reflects a change in foreign policy priorities for the second term.
Rhodes said all three nominees share Obama's basic view of the world and America's place in it, a view that favors multilateral alliances and a reliance on intelligence and lethal technology, holding war as a last resort. "These are three men well suited to that task," he said.
Brennan has led a White House effort to develop a "playbook" of counterterrorism policies, aiming to set up institutions that can sustain the fight against al-Qaeda for another decade or more. But Obama is also seeking to turn toward other objectives, including new initiatives in Asia and expanded nuclear-nonproliferation work.
Hagel would add a well-known war skeptic to the administration's national security team at a time when a potential military confrontation with Iran over its uranium-enrichment efforts looms as one of the gravest security challenges of Obama's second term.
A former Republican senator from Nebraska, Hagel supported the Iraq invasion in 2003. But he later broke with his party leaders over the war's management.